Harnessing Nitrogen and Water Management to Improve Resource Use Efficiency in Tomatoes.

In agricultural systems, soil water availability and irrigation frequency are important to maintain plant C assimilation capacity, growth and productivity. Similarly, soil N management and availability affects crop performance. In regions where water is limiting, management strategies that fine-tune the interaction between water and N are crucial to increase efficiency in resource use. In this study we evaluated how nitrogen availability (low and high) and irrigation frequency (every day or every ~5 days) affected root hydraulic conductivity and leaf gas exchange in tomato plants grown under greenhouse conditions. We found that root hydraulic conductivity was higher in plants grown under high N conditions and was not affected by water treatment. As expected, assimilation rate and stomatal conductance were higher in plants irrigated daily and receiving sufficient N; however, this led to a decrease in water use efficiency. Plants grown under infrequent irrigation and high N conditions had the lowest stomatal conductance and higher water use efficiency. Leaf relative water content was lower in plants with high N and infrequent watering, suggesting increased and unmet water demands likely associated with increases in biomass and transpiration. In fact, biomass production was more affected by N availability than by watering regime. Our results highlight the importance of managing both resources, water and N, together to improve their use efficiency. Higher N availability increases the root water uptake capacity but also water demands due to a larger canopy, which may be counterproductive under water limited conditions and result in transient plant water stress and lower productivity.